Sometime ago I made a 69" spitfire from plans and I planked the fuz as there was no way it could be done using sheet balsa , what I did was this ,,(it does work for a boat hull ) firstly the first few planks run straight then when they with start to taper as the shape follows the hull /fuselage ,these strips will overlap the last and it where they intersect is what you cut off ,no need to measure use a straight edge place it on the bottom of the last plank draw a line onto the next plank and that is what you cut .Full size boats don't have planking running full length in on piece. + the length and shape will determine the width and thickness ,bit hard to explane but once you try this method does work ,Google pics or planked hulls .......mark